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Help in Op Amp circuit design

Discussion in 'Homework Help' started by rhaeg, Apr 30, 2016.

  1. rhaeg

    rhaeg New Member

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    Hello,

    Im new to this forum and a student of electronics,

    I need help to realize an op-amp based circuit that will satisfy the following input-output transfer characteristic



    ecda0b59-ac7a-40c6-8377-aa8036e0b539.jpg

    The sole requirement is to design an opamp based circuit with the least number of opamps

    Thank you very much!
     
    Last edited: Apr 30, 2016
  2. Inquisitive

    Inquisitive Super Moderator

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    Hi rhaeg,

    Welcome to the forum. Enjoy your stay here.
     
    • Thanks Thanks x 1
  3. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    And it sounds like we would be doing your homework for you if we just handed you a circuit...

    We have a "Homework Help" forum for this.
     
  4. dave

    Dave New Member

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  5. JimB

    JimB Super Moderator Most Helpful Member

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    ONLINE

    rhaeg
    If this a school/college/university assignment, please let us know and I (or one of the other Moderators) will move it to the correct forum.

    JimB
     
  6. rhaeg

    rhaeg New Member

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    It is indeed, a university exercise for practice,
    i have tried different solutions, however, currently stuck.

    Please do move it,

    Thank you and sorry for the hustle.
     
  7. Inquisitive

    Inquisitive Super Moderator

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    Moved to Homework Help...
     
  8. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    A modification of the circuits presented here might be suitable...
     
  9. rhaeg

    rhaeg New Member

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    So, currently my only guess is the attached circuit,
    this is only for the first stage (negative voltages), i realize that another stage should be added.

    However, the characteristic is very far from what is required.
     

    Attached Files:

  10. rhaeg

    rhaeg New Member

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    So, having tried to follow the lead of MikeMI,
    i'm getting closer, currently, i am able to get the correct behavior for positive voltages, i.e (almost) linear follow upto 7V saturation, and then constant 7V.
    However, still unable to get the correct behavior on the negative side.

    https://drive.google.com/open?id=0Bz_wXxVGER4UeXM1cmpLU0pvSEk

    A question on that note,
    what determines the voltage at which the opamp goes into saturation?

    i attach the circuit in ltspice.
     

    Attached Files:

    Last edited: Apr 30, 2016
  11. Les Jones

    Les Jones Well-Known Member

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    Try googling for "precision rectifier" This should help you with the part of the transfer function between -8 and + 8 volts. I will leave you to work out how to deal with the parts between -15 and -8 volts and between + 8 and + 15 volts.

    Les.
     
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  12. rhaeg

    rhaeg New Member

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    Thank you! That hint got me going on the right way and i found that characteristic to be the one of a Full Wave Rectifier.

    After simulation of the op amp based circuit i am able to get the correct characteristic.

    [​IMG]

    However, i still have one problem,
    is there a way to control the gain regardless of the power supply used for the Op Amps?
    I am currently able to get a maximum voltage of 8V when setting the power supply to +-9.5V,
    can i get the same with a supply of +-15V?
     

    Attached Files:

  13. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Is the TL082 rail to rail?
     
  14. Les Jones

    Les Jones Well-Known Member

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    Hi MikeMl,
    Apologies for giving basically the same in my post #10 as you had given in your post #7. I only noticed it today .
    rhaeg,
    I suspect using the rail voltage to limit the output may not be acceptable as a solution. I also suspect the classic zener diode in the feedback may also be unacceptable as it would require selecting an 8.2 volt zener that was at the low end of its tolerance. I can think of a way that would probably work using one extra op amp but I can't think a hint. (Other than giving you the full idea.)

    Les.
     

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